Recombinant adenoviruses have emerged as attractive vehicles for in vivo gene transfer to a wide variety of cell types. The first generation vectors, which are rendered replication defective by deletion of the immediate early genes E1a and E1b, are capable of highly efficient in vivo gene transfer into nondividing target cells [M. Kay et al, Proc. Natl. Acad. Sci. USA, 91:2353-2357 (1994); S. Ishibashi et al, J. Clin. Invest., 92:883-893 (1993); B. Quantin et al, Proc. Natl. Acad. Sci. USA, 89:2581-2584 (1992); M. Rosenfeld et al, Cell, 68:143 (1992); R. Simon et al, Hum. Gene Thera., 4:771 (1993); Rosenfeld et al, Science, 252:431-434 (1991); Stratford-Perricaudet et al, Hum. Gene Ther., 1:241-256 (1990)].
Immune responses of the recipient to the viral vector, the transgene carried by the vector, and the virus-infected cells have emerged as recurring problems in the initial application of this technology to animals and humans [Yang et al, J. Virol., 69:2004-2015 (1995) (Yang I)]. In virtually all models, including lung-directed and liver-directed gene therapy, expression of the transgene is transient and associated with the development of pathology at the site of gene transfer.
The transient nature of transgene expression from recombinant adenoviruses is due, in part, to the development of antigen specific cellular immune responses to the virus-infected cells and their subsequent elimination by the host. Specifically, first generation vectors, although deleted in the E1a region of the vector, express viral proteins in addition to the transgene. These viral proteins activate cytotoxic T lymphocytes (CTL) [(Y. Dai et al, Proc. Natl. Acad. Sci. USA, 92: 1401-1405 (1995); Y. Yang et al, Proc. Natl. Acad. Sci. USA, 91:4407-4411 (1994) (Yang II); and Y. Yang et al, Immunity, 1:433-442 (1994) (Yang III)]. The collaboration of CTLs directed against newly synthesized viral proteins and viral specific T helper cells [Zabner et al, Cell, 75:207-216 (1993); Crystal et al, Nat. Genet., 8:42-51 (1994)] leads to the destruction of the virus-infected cells.
Another antigenic target for immune mediated clearance of virally-infected cells can be the product of the transgene when that transgene expresses a protein that is foreign to the treated host. CTLs are thus an important effector in the destruction of target cells, with activation occurring in some cases in the context of the transgene product, or of the viral-synthesized proteins, both of which are presented by MHC class I molecules [Yang I; and Zsengeller et al, Hum. Gene Thera., 6:457-467 (1995)]. These immune responses have also been noted to cause the occurrence of associated hepatitis that develops in recipients of in vivo liver directed gene therapy within 2-3 weeks of initial treatment.
Another limitation of recombinant adenoviruses for gene therapy has been the difficulty in obtaining detectable gene transfer upon a second administration of virus. This limitation is particularly problematic in the treatment of single gene inherited disorders or chronic diseases, such as cystic fibrosis (CF), that will require repeated therapies to obtain life-long genetic reconstitution. Diminished gene transfer following a second therapy has been demonstrated in a wide variety of animal models following intravenous or intratracheal delivery of virus [T. Smith et al, Gene Thera., 5:397 (1993); S. Yei et al, Gene Thera., 1:192-200 (1994); K. Kozarsky et al, J. Biol. Chem., 269:13695 (1994)]. In each case, resistance to repeated gene therapy was associated with the development of neutralizing anti-adenovirus antibody, which thwarted successful gene transfer following a second administration of virus.
Potential solutions for these problems have been directed towards the development of second generation recombinant viruses [Y. Yang et al, Nat. Genet., 7:362-369 (1994) (Yang IV); and J. Engelhardt et al, Hum. Gene Thera., 5:1217 (1994)] designed to diminish the expression of newly synthesized viral proteins, and the use of non-immunogenic transgenes, to prevent CTL activation.
Thus, there remains a need in the art for a method and composition for improving the efficiency of gene transfer during repeated administrations of viral gene therapy.